 /*******************************************************************************
  * Copyright (c) 2000, 2005 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.indexing;

 import java.util.Observable ;

 public abstract class Page extends Observable implements Referable {

     public static final int SIZE = 8192;

     protected int pageNumber;
     protected int referenceCount;
     protected Buffer pageBuffer;
     protected PageStore pageStore;

     /**
      * Constructs a new page of the given size.
      */
     public Page(int pageNumber, PageStore pageStore) {
         this.pageNumber = pageNumber;
         this.pageStore = pageStore;
         this.referenceCount = 0;
     }

     /**
      * Adds a reference for this entity to track.
      */
     public int addReference() {
         referenceCount++;
         return referenceCount;
     }

     /**
      * Returns the page number of the page.
      */
     public int getPageNumber() {
         return pageNumber;
     }

     /**
      * Tests for existing references.
      */
     public boolean hasReferences() {
         return referenceCount > 0;
     }

     /**
      * Releases a page back to the store.
      */
     public void release() {
         pageStore.release(this);
     }

     /**
      * Removes a reference.
      */
     public int removeReference() {
         if (referenceCount > 0)
             referenceCount--;
         return referenceCount;
     }

     /**
      * Writes the contents of the page to a buffer.
      */
     public abstract void toBuffer(byte[] buffer);

 }

